(1) Field of the Invention
The present invention relates to an image forming apparatus, and relates in particular to an image forming apparatus including a mechanism that forces a developing unit towards a photosensitive unit so as to maintain, at a specified value, a gap between a photosensitive drum and a developing roller.
(2) Description of the Related Art
An electrophotographic image forming apparatus forms an image by supplying toner to an electrostatic latent image from a developing roller included in a developing unit to develop the electrostatic latent image into a toner image, and transferring the toner image onto a recording sheet. Here, the electrostatic latent image is formed by performing exposure-scanning on an outer circumferential surface of a photosensitive drum.
In order to form a preferable toner image on an outer circumferential surface of the photosensitive drum, it is necessary to maintain, at a specified value, a gap between an outer circumferential surface of the developing roller and an outer circumferential surface of the photosensitive drum (hereinafter, “developing gap”). The following shows how the developing roller and the photosensitive drum are conventionally arranged so that the developing gap is set to the specified value. A roller for adjusting the developing gap (DS roller) is attached to a shaft of the developing roller. Here, the DS roller has a diameter slightly larger than a diameter of the developing roller. The developing roller is forced towards the photosensitive drum so that an outer circumferential surface of the DS roller makes contact with the outer circumferential surface of the photosensitive drum. Here, “to force” means to apply pressure in a predetermined direction.
In recent years, in order to facilitate maintenance, there has been known an image forming apparatus having a structure in which the developing roller and its peripheral members and the photosensitive drum and its peripheral members are formed into a developing unit and a photosensitive unit respectively so as to be detachable from a body of the image forming apparatus.
However, when the image forming apparatus having such a structure is delivered to a customer, the following problem possibly arises. That is, the developer vibrates badly in a vertical direction in sympathy with vibration during transportation of the image forming apparatus, which causes toner stored in the developing unit to spill out of an opening for the developing roller, resulting in a mess in the image forming apparatus.
In order to solve the above-stated problem, Japanese Patent Application Publication No. 2000-19839, for example, recites the following. Firstly, a developing unit having a developing roller and its peripheral members is detached from the body of the image forming apparatus. Next, a cover is attached to an opening for the developing roller so as to be covered. Then, the developing unit is delivered packaged separately from the body of the image forming apparatus.
According to a delivering method recited in Japanese Patent Application Publication No. 2000-19839 as shown above, the developing unit is packaged separately from the body of the image forming apparatus. Therefore, in this case, a delivery cost increases due to packaging material and labor necessary for packaging, and delivery efficiency decreases due to an increase in an overall packaging size of the image forming apparatus. Furthermore, when the image forming apparatus is delivered, it takes time to set up the image forming apparatus since it is necessary to unpackage the developing unit and mount the developing unit in the body of the image forming apparatus.